SRT files w/ foreign characters & SRT file name conventions

I want to create SRT files for captions in a number of different languages, including some which do not use an English alphabet character set, such as Chinese and Vietnamese. I have someone working on the translations for these, and I understand the basic layout/conventions of the SRT file, but ...

* Once I cut and paste my Chinese and Vietnamese characters into a document, when I go to save it as a TXT file, how do I do this so that it saves the characters/fonts for these langagues? My understanding is that when I do a 'save as' in Word, there are some encoding options that come up for saving it to Txt, and I just have to pick the 'unicode' option. Is that about it?

* And, once I've saved my .txt file and then changed the file name to an SRT extension, how does either my editing program and/or the 'hosting' venue (e.g. YouTube, Vimeo) know that a particular caption is for a particular language - how does it know that 01.srt is Chinese and that 02.srt is Spanish, and so forth?

I've read that there are language/country naming conventions for SRT files - such as:

vi_VN for Vietnamese, and zh_CN for Simplified Chinese, and so forth. But does this mean that for my Chinese caption, I'd simply name it:

zh_CN.srt? And that by doing this, people watching will have the option to select simplified Chinese captions and that this is file that will be used for those captions?

Thanks, David.